Google's Glass team made it clear in a post on Google+ that the product is still in beta testing and the company's looking for early adopters, also known as Explorers, while engineers continue to work on the hardware and software and third parties add to the ecosystem of apps.

"Last week, we told you we'd be trying out new ways to find Explorers," the team wrote in the blog post. "Well, we weren't kidding. We learned a lot when we opened our site a few weeks ago, so we've decided to move to a more open beta."

For now, Glass is only available for sale in the United States, though the team noted in comments on the blog post that it hopes to make Glass more widely available "in the future." The team didn't specify a timeframe.

By this spring, it was generally thought that Google had 8,000 to 10,000 Explorers on board.

Then on April 15, Google gave U.S. users the chance to buy Glass during a one-day sale. Customers had to pay $1,500 for the digital eyewear and could choose their own design of prototype. Google declined to say how many pairs it sold that day.

The wearable computers have a transparent display over the right lens and enable users to take photos, shoot video, search the Web, send email, and share images and info across social networks. Glass, which can be controlled by voice, touch, and gesture, has a growing ecosystem of apps from partners like Facebook, CNN, Twitter, and Elle.